Re: [libgpiod] bug: pull-up does not work

["Jiří Prchal" <jiri.prchal@aksignal.cz>]

On 25. 03. 22 17:01, Kent Gibson wrote:
> On Fri, Mar 25, 2022 at 04:13:11PM +0100, Jiří Prchal wrote:
>>
>>
>> On 25. 03. 22 15:57, Kent Gibson wrote:
>>> On Fri, Mar 25, 2022 at 11:02:07AM +0100, Jiří Prchal wrote:
>>>> Hi,
>>>> since in debian is 1.6.2 and pull-up doesn't work so I cloned git, branch
>>>> next/libgpiod-2.0 and compiled libgpiod and tools, but no luck, same result.
>>>>
>>>
>>> You mean it doesn't work for you on your platform.
>>>
>>> The libgpiod-2.0 branch is a work in progress and should not be considered
>>> the place to go to find solutions to problems with v1.6.
>>> Not that I'm saying that the v2 branch doesn't work, I'm actually pretty
>>> sure it does, but its purpose is to switch to the latest kernel uAPI, not
>>> to provide fixes, should they be needed, for v1.6.
>> Just thought api v1 doesn't support pull-ups so tried v2.
> 
> v1 does support bias since Linux v5.5, and libgpiod added support in v1.5.
> 
>>>
>>>> ~# uname -r
>>>> 5.17.0-rc7_cpm9g25
>>>>
>>>> floating pins should go with pull-up/down
>>>> ~# gpioget -B pull-up 3 6 8 10 12 14 16 18 20
>>>> 0 0 0 0 0 0 0 0
>>>> ~# gpioget -B pull-up 3 6 8 10 12 14 16 18 20
>>>> 1 1 0 0 0 0 0 0
>>>> ~# gpioget -B pull-up 3 6 8 10 12 14 16 18 20
>>>> 0 1 0 1 0 0 0 0
>>>>
>>>> ~# gpioget -v
>>>> gpioget (libgpiod) v2.0-devel
>>>>
>>>> Whats wrong with it?
>>>
>>> You forgot to mention which of those pins are floating.
>> All of them.
>>> Or what gpiochip3 is and whether it supports biasing.
>> AT91SAM9G25, hw supports pull-ups.
>>>
>>> So does your chip support pull-up/down?
>>> The kernel can only enable it if the hardware and pinctrl driver supports it.
>> Is there possibility that pinctrl doesn't support it? I think other gpios
>> used in kernel are with pull-up.
>> Example:
>> pinctrl@fffff400 {
>> 	1wire {
>> 		pinctrl_1wire: 1wire-0 {
>> 			atmel,pins = <AT91_PIOC 0 AT91_PERIPH_GPIO AT91_PINCTRL_PULL_UP>; /* PC0
>> PIO, pull-up */
>> 		};
>> 	};
>> };
>>
> 
> Pinctrl and device tree are outside my area, but my understanding is
> that setting via DT is a separate interface, so while it may be
> supported by DT it may not be via the gpiolib interface.
> But I will defer to anyone else on that.
> (CCing in Andy since I'm pretty sure he would know)
> 
> Not sure which pinctrl is relevant for your case.
> pinctrl-at91 doesn't appear to support setting the pull-up via the gpiolib
> interface, but pinctrl-at91-pio4 does, so my guess would be you are using
> the pinctrl-at91.
pinctrl-at91-pio4 didn't help, syminfo says "for Atmel PIO4 controller 
available on sama5d2 SoC" but my is sam9g25.
How can I find out if it supports gpiolib?
> 
> But again, this is outside my area so you would need to confirm that
> yourself or get feedback from someone else.
> If you determine that you are using a pinctrl that supports setting
> bias via gpiolib then we'll have to do some more digging.
> 
> Cheers,
> Kent.
> 
Thanks
Jiri